Predictive Direct Power Control Research Articles

An Improved P-DPC for A New Inverter Based on MLD Model

Building an accurate mathematical model for inverter is the key to achieving a precise control. Contrasted to the traditional switching function model of power electronic circuits, this paper built the mixed logical dynamic(MLD) model for a new inverter, and the MLD model was used as a prediction model, then a predictive direct power control(P-DPC) method was researched for the new inverter. A symmetrical 4+4 voltage vector sequence was employed to obtain constant switching frequency and lower THD of output voltage, the action time of vector sequence was calculated by minimizing objective function. The feasibility and effectiveness were proved by simulations.

Predictive Approach for Power Quality Improvement Based Direct Power Control

The extensive use of non-linear loads in industry becomes increasingly a serious problem that affects the quality of energy delivered to customers. Therefore, the shunt active power filter (SAPF) has emerged as an important industrial tool to eliminate induced harmonic currents and compensating of reactive power. This paper proposes an improved control configuration for SAPF based on a modern technique called predictive direct power control (Predictive-DPC). The principle of this control is based on the direct regulation of the instantaneous active and reactive powers to guarantee a good energy quality on the grid side. For this purpose the appropriate average voltage vector which cancels power tracking errors is calculated by a simple predictive model at the bigining of each control period. This type of control includes various features such as the lack of look up table (LUTs) and closed current loops and the constant switching frequency is achieved through the use of PWM modulation. The results of the simulation process show a high performance in the steady and transient state function for predictive-DPC control that might be a reasonable alternative to conventional DPC in the field of active power filtering.

A performance assessment of model predictive direct power control and model predictive direct current control for switched reluctance motor drive systems

In this paper, a performance assessment between model predictive direct power control and model predictive direct current control is proposed by using a simplified computational approach for switched reluctance motor drive systems. To reduce the calculation efforts, a reduced set of switching states is employed by combining the space vector modulation strategy with the dead‐beat predictive control technique. Specifically, an optimal state of the reduced set of switching states is directly selected and applied in neutral point clamped active front‐end rectifiers of switched reluctance motor drive systems. In comparison with the conventional method, the proposed scheme takes into account the 27 candidate switching states to 10. The number of admissible switching states is drastically reduced, which saves the execution time by up to 45% for model predictive direct power control and up to 56% for model predictive direct current control. The unwanted exploration for all available voltage vectors can be eliminated while the flying capacitor voltages are maintained balanced. Meanwhile, the use of the well‐known modulation methods can be avoided by the proposed strategy, thus enhancing the dynamic performance. Simulation results obtained with the neutral point clamped active front‐end rectifiers confirm the efficacy of two proposed methods. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Model Predictive Direct Power Control for Single Phase Three-Level Rectifier at Low Switching Frequency

This paper presents a new model predictive direct power control (MP-DPC) to overcome the drawbacks of model predictive control (MPC) for single phase three-level rectifiers in the railway traction drive system, including huge online calculation, poor power control precision at the low switching frequency and variable switching frequency. To do so, an exact analytical solution of instantaneous power estimation is adopted to predict active and reactive powers in next duty cycle updating interval for achieving the deadbeat control and reducing the predictive error at the low switching frequency (below 1 kHz). The optimal d -axis and q -axis components of input voltage within next duty cycle updating interval of the adopted rectifier in rotating coordinate system are directly calculated by minimizing the cost function. And the optimal drive pulses are generated by pulse width modulation stage in the proposed MP-DPC, other than evaluating cost function for each voltage vector in traditional MP-DPC. Finally, the influence of inductance mismatch on control system is analyzed, and an inductance estimation method is shown to improve the control precision. An experimental comparison with other five different DPC schemes has verified the effectiveness of the proposed MP-DPC scheme.

Finite‐state model predictive power control of three‐phase bidirectional AC/DC converter under unbalanced grid faults with current harmonic reduction and power compensation

Under unbalanced grid fault conditions, the current harmonic contents of a three-phase bidirectional AC/DC converter increase significantly and twice grid-frequency ripples exist in both active power and reactive power, which influence the output power quality of the converter. Compared with the conventional finite-state model predictive direct power control (MPDPC), the MPDPC with power compensation (MPDPC-PC) method is proposed for the three-phase bidirectional AC/DC power converter to reduce harmonic currents and output power ripples without extraction of complex positive/negative sequences from the grid voltage/current and phase-locked loop. The power compensation values are expressed by grid voltages and their quadrature signals that lag 90 electrical degrees in the αβ stationary coordinates system. MPDPC-PC exhibits better performance by reducing the harmonic contents of grid currents and eliminating active power or reactive power ripples of the three-phase bidirectional AC/DC converter with flexible reactive power compensation capability. Compared with the MPDPC and linear current control schemes, experimental results confirm the effectiveness of the designed method under unbalanced grid conditions.

Predictive Direct Power Control Technique for Voltage Source Converter With High Efficiency

A predictive direct power control (PDPC) technique to decrease switching loss by injecting offset voltage is proposed for three-phase voltage source converters. The active and reactive power elements of the converter are directly controlled by using three-phase future converter input voltages, which are modified for lowering switching losses by injecting a future offset voltage. Switching operations, generated by the developed PDPC algorithm with modified converter voltage, stop switching operation in one of the converter phases exposed to the highest input current. The non-switching period and the non-switching phase in the proposed technique is automatically adjusted by the reactive power reference, which leads to high efficiency, irrespective of varying input power factor angle condition. The proposed algorithm chooses one optimal voltage vector enabling future active and reactive power to approach closest to the future power references and prohibiting switching of one converter phase conducting the highest current at each step. Therefore, the developed technique can directly control power components and increase converter efficiency, which is proven by simulation and experimental verification.

Finite States Model Predictive Control for Fault-Tolerant Operation of a Three-Phase Bidirectional AC/DC Converter Under Unbalanced Grid Voltages

The bidirectional ac/dc converter is widely used to realize the power conversion between ac and dc microgrid, but the faults of switch devices and unbalanced grid voltages may lead to the decline of power quality and affect normal operation of the converter. The four-switch three-phase (FSTP) fault-tolerant structure is reconstructed from a six-switch three-phase structure with switch device fault. In order to reduce harmonic currents and output power fluctuations under unbalanced grid voltages, finite states model predictive direct power control (MPDPC) with power compensation method is proposed for FSTP structure and predictive power model of the bidirectional FSTP ac/dc converter is established. The power compensation values are expressed by grid voltages and their quadrature signals that lagging 90 electrical degrees in the αβ stationary coordinate system. Compared with the conventional method, phase-locked loop, pulse width modulation, and complex positive-/negative-sequence extraction of grid voltage are not required. Ripples of active power or reactive power under unbalanced grid voltages are eliminated. The proposed fault-tolerant MPDPC with power compensation method ensures the continuous and reliable operation of the bidirectional ac/dc converter with high power quality. Simulation and experimental results are presented to validate the proposed control strategy under symmetrical unbalanced grid voltages with switch device faults.

Predictive Direct Power Control (PDPC) of Grid-connected Dual-active Bridge Multilevel Inverter (DABMI)

This paper deals with controlling a grid-connected dual-active bridge multilevel inverter for renewable energy integration. The concept of direct power control is integrated with model predictive control algorithm, which is termed as predictive direct power control, to control the real and reactive power injected into the power grid. The proposed multilevel inverter allows more options of feasible voltage vectors for switching vector selections in order to generate multilevel outputs, and thereby obtaining high power quality in the power grid. By using the predictive direct power control, simulation results show that the proposed multilevel inverter produces lower power ripple and manage to achieve currents with low total harmonic distortion which are well within the IEEE standard. The modeling and simulation of the system are implemented and validated by MATLAB Simulink software.

A power quality enhanced grid voltage sensorless predictive direct power control for active front end rectifiers

In this research work, a power quality enhanced grid voltage sensorless deadbeat predictive direct power control (DB-DPC) approach for AC/DC power converters based on latest virtual flux (VF) estimation, DB-DPC and space vector pulse width modulation (SVPWM) is proposed. At first, the grid voltage sensorless technique with switching table based DPC, which is a conventional approach, is discussed and its performance is analyzed under both increase of load as well as decrease of load conditions. Further, the proposed technique performance is also analyzed under the same circumstance and its performance is compared with the traditional method. The proposed technique has numerous advantages over the conventional method such as constant switching frequency, better active and reactive power control, good regulation of dc bus voltage, and enhanced power quality performance. As the proposed approach utilizes VF, DB-PC, and SVPWM techniques, this ensure line voltage sensorless approach, excellent control dynamics and constant switching frequency, respectively. At the end, experimental validation is done to confirm the supremacy of the proposed technique under load varying conditions and has a phenomenal performance under these circumstances.

Predictive model approach based direct power control for power quality conditioning

This paper has presented improved control structure based direct power control (DPC) applied for shunt active power filtering. Basically, DPC control strategy employs instantaneous active and reactive power terms as controlled variables. This work introduces an integration concept of predictive control algorithm for shunt active power filter system application. Process of this latter adopts discrete model of PWM converter in the aim to predict future behaviour of the system. Switching vector selection principles for predictive control is very different compared to conventional method. For conventional DPC the selection is performed via heuristic switching table while predictive DPC algorithm takes on an optimized way based on cost function minimization depending to power errors, this latter evaluate the effects of each active voltage vector and the one reducing the cost function is chosen to be applied in the next sampling period. The application of optimal switching state leads to regulate the input active and reactive power which resulted in the cancellation of harmonic power component contained in the network. Simulation results are presented to verify the validity and effectiveness of the proposed predictive DPC in terms of dynamic and steady state performance for shunt active power filtering application.

Finite-Set Model Predictive Direct Power Control of Grid Connected Current Source Inverter

This paper proposes a novel control strategy for grid connected current source inverter (CSI) without using a phase locked loop (PLL). The proposed finite set model predictive direct power control (FS-MPDPC) is based on direct power control (DPC) and model predictive control (MPC), and it is introduced for the first time for CSIs. The FS-PDPC controls separately the active and reactive power, using an appropriate discrete-time prediction model to predict the future behaviour of the powers to be injected into the grid, and a cost function for the selection of the optimal control signals to be applied on the switches of the power converter. The proposed control technique is simulated in Matlab/simulink® software. The obtained results verify the effectiveness of this method during different test.DOI: http://dx.doi.org/10.5755/j01.eie.23.5.19240

Analysis and experimental evaluation of shunt active power filter for power quality improvement based on predictive direct power control.

This paper discusses the use of the concept of classical and predictive direct power control for shunt active power filter function. These strategies are used to improve the active power filter performance by compensation of the reactive power and the elimination of the harmonic currents drawn by non-linear loads. A theoretical analysis followed by a simulation using MATLAB/Simulink software for the studied techniques has been established. Moreover, two test benches have been carried out using the dSPACE card 1104 for the classic and predictive DPC control to evaluate the studied methods in real time. Obtained results are presented and compared in this paper to confirm the superiority of the predictive technique. To overcome the pollution problems caused by the consumption of fossil fuels, renewable energies are the alternatives recommended to ensure green energy. In the same context, the tested predictive filter can easily be supplied by a renewable energy source that will give its impact to enhance the power quality.

Dead‐beat predictive direct power control of voltage source inverters with optimised switching patterns

This study presents a novel dead-beat predictive direct power control (PDPC) strategy working at nearly constant switching frequency for the voltage source inverter. The proposed strategy employs two active voltage vectors and one null voltage vector during every control period. To solve the problem of negative predicted duration time of active voltage vectors in the conventional dead-beat PDPC strategy, an automatic updating mechanism is designed. When the predicted duration time is negative, the applied voltage vectors will be updated automatically without the need of reselecting voltage vectors or recalculation of the duration time. Accurate tracking of both active and reactive power can be achieved with small power ripples using the strategy proposed in this study. The proposed PDPC strategy shows excellent steady performance and fast dynamic responses. High sampling frequency can also be avoided and the calculation process is simple enough to be implemented on normal DSPs. Simulation and Experimental results are presented to validate the feasibility of the proposed dead-beat PDPC strategy.

A Model-Based Predictive Direct Power Control for Traction Line-Side Converter in High-Speed Railway

With the rapid development of China high-speed railway, the low frequency oscillation (LFO) of electrical quantities appears more often recently and leads to some severe problems of train operation. To improve the traction line-side converter control and suppress the phenomenon economically and effectively, a model-based predictive direct power control (MPDPC) approach is proposed in this paper. The approach adopts a discrete-time model of traction line-side converter in d-q reference frame to predict the future values of the input active and reactive power. The optimal switching state is selected by minimizing a cost function of power to evaluate the power errors at the next sampling time. Through the theoretical analysis and simulations, the performance of MPDPC is compared with traditional transient direct current control (TDCC) that is widely adopted in China Railway High-Speed 3 electric-multiple-unit. The real-time online simulations based on Real-Time Laboratory (RT-LAB) are also realized to further validate the results. Moreover, two vehicle-grid cascade simulation systems are constructed, and the LFO suppressing capability of MPDPC and TDCC is compared. Finally, the steady-state characteristic, dynamic characteristic, and LFO suppressing capability of MPDPC are demonstrated through the analysis of key performance indexes.

Simulation and real time implementation of predictive direct power control for three phase shunt active power filter using robust phase-locked loop

This paper proposes a predictive direct power control for shunt active power filters. The main goal of the proposed active filtering system is to eliminate the unwanted harmonics and compensate fundamental reactive power drawn from the non-linear loads. The proposed control is characterized by a high transient dynamic, which makes it an interesting alternative for classic direct power control. In order to improve the efficiency of the proposed control, different simulation and experimental tests were carried out with real time implementation on dSPACE 1104 card in steady and transient states. The obtained results indicate closeness between simulation and experimental tests, which prove and verify the effectiveness of the proposed control strategy.

Model Predictive Direct Power Control for Nonredundant Fault Tolerant Grid-Connected Bidirectional Voltage Source Converter

This paper proposes a model predictive direct power control scheme for nonredundant fault tolerant grid-connected bidirectional voltage source converter (BVSC) with balanced dc-link split capacitor voltage and high reliability. Based on the operation analysis of fault-tolerant BVSC with phase leg faults, a power predictive model of three-phase four-switch fault-tolerant topology in αβ coordinates is established, and the space voltage vectors with unbalanced dc-link split capacitor voltage are analyzed. According to the power predictive model and cost function, the optimal space voltage vector is selected to achieve a flexible, smooth transition between inverter and rectifier mode with direct power control. Pulse width modulation and phase locked loop are not required in the proposed method. The constraint of dc-link voltage constraint is designed for the cost function to achieve a central point of dc-link voltage offset suppression, which can reduce the risk of electrolytic capacitor failure for over-voltage operation. With the proposed control method, the converter can work continuously in both inverter mode and rectifier mode, even if phase leg faults occur. The simulation and experimental results show good steady-state and dynamic performance of the proposed control scheme to enhance the reliability of bidirectional power conversion.

Research on Compound Control Strategy of MMC - HVDC System

In this paper, the predictive direct power control (PDPC) algorithm using the combination of MPC and VF estimation method is proposed. The mathematical model of MMC-HVDC in the  coordinate system is analyzed. The DSOGI-QSG is used to improve the reliability and accuracy of VF estimation. Adopt predictive method to achieve optimal balanced capacitor voltage and the finite set optimization is used to optimize reference voltage of the converter. Finally, a 21- level MMC-HVDC system is built to verify the control strategy on the PSCAD-EMTDC platform. The simulation results show that this method can achieve the following goals, decoupling active and reactive power, faster responding to power change disturbance; restraining circulating current effectively, improving the capacitor voltage balancing and DC side voltage stability.

Model Predictive Direct Power Control of Doubly Fed Induction Generator with Dead-Time Compensation

The paper presents the control of a doubly fed induction generator connected with a three-level neutral point clamped inverter with compensation of dead-time effects. The principle of the proposed control scheme is to use the dynamical model to compute predictions of the future values of the stator flux, rotor current and DC-link capacitor voltages for all possible configurations of voltage vectors. However, the dead-time to avoid the short circuit in the inverter also causes the modeling errors. Thus, by taking into account the dead-time in the model, it is possible compensate the dead-time effect of the switching devices. The active and reactive powers can be estimated based on the stator flux and the rotor current. The cost function considers the error between the active, reactive powers and their references, balance the DC-link capacitor voltage and reduce the switching frequency and common-mode voltage. The optimal switching state that minimizes the cost function is selected and applied to the inverter. The simulation results were carried out with Matlab under different conditions of wind speed and verifying the effectiveness of the proposed method.

Improved Predictive Direct Power Control of Doubly Fed Induction Generator During Unbalanced Grid Voltage Based on Four Vectors

This paper presents an improved strategy in the field of predictive direct power control (PDPC) of the doubly fed induction generator (DFIG). The proposed strategy applies four voltage vectors in every period in order to have constant switching frequency and low current total harmonic distortion. The appropriate voltage vectors in each period are recognized when estimated duration times of selected active vectors are positive. The suggested technique shows excellent performance during transient and steady-state conditions. The proposed PDPC can easily follow the power references under normal and abnormal voltage conditions even if the power references contain ac terms. Without any additional controller, the proposed technique could obtain smooth stator active and reactive powers or smooth electromagnetic torque, or could inject sinusoidal and balanced currents into the grid when the unbalanced voltage appears in DFIG stator windings. Simulation studies for this technique are carried out for 2-MW DFIG in MATLAB Simulink environment under balanced and unbalanced grid voltage. The results of this technique under unbalanced grid voltage are compared with two other previous PDPC strategies. Comparisons show that the performance of the proposed strategy under unbalanced grid voltage is superior to the two other strategies.

Nonlinear Direct Control for Three-Level NPC Back-to-Back Converter PMSG Wind Turbine Systems: Experimental Assessment With FPGA

Finite control set model predictive control techniques have been emerged as good alternatives in particularly for multilevel and multiphase power converters, for which switching vectors with multiple magnitudes/directions are available but the modulator or switching table design becomes complex. In this paper, a finite-control-set model predictive direct torque and power control (FCS-DTC-DPC) for grid-tied three-level neutral-point clamped back-to-back power converters in permanent-magnet synchronous generator wind turbine systems is presented and experimentally compared with its counterpart: switching table-based direct torque and power control (ST-DTC-DPC). Both methods have been implemented and verified at a lab-constructed setup with a fully FPGA-based real-time controller. Experimental results confirm that both achieve (equivalently) good control dynamics, whereas FCS-DTC-DPC outperforms ST-DTC-DPC in terms of steady-state control performances at similar switching frequencies but has a higher computational demanding and is more sensitive to system parameter variations.